1. Field of Invention
The present invention relates to organic light emitting diode (OLED) device. More particularly, the present invention relates to an organic light emitting diode (OLED) device having a light emitting layer fabricated by doping an organic material layer with hole transporting material and phosphorescent material.
2. Description of Related Art
Due to rapid growth in the communication industry, portable equipment is a major center of development. Flat displays have become the principal human-machine interface. In general, flat panel displays are divided according to the types of techniques into plasma display panel (PDP), liquid crystal display (LCD), electro-luminescent display, light emitting diode (LED), vacuum fluorescent display, field emission display (FED), electro-chromic display and organic light emitting diode (OLED) display. Among various types of displays, organic light emitting diode (OLED) display has the greatest potential to become the dominant flat panel display in the next generation. An OLED display has many advantages including self-illuminating, no viewing angle retention, low energy consumption, easy to fabricate, low production cost, low operating temperature, quick response and full coloration.
An OLED device utilizes the self-illuminating property of organic functional materials to form images. According to the molecular weight of the organic functional material, OLED displays can be classified into small molecule OLED (SM-OLED) and polymer light-emitting device (PLED).
In general, luminance and light-emitting efficiency are the two major criteria for determining the quality of an OLED device. Researchers are always trying to increase the luminance and efficiency of OLED devices.
At present, the light-emitting layer inside the OLED display is made using fluorescent materials. However, fluorescent materials can hardly reach the desired level of luminance and efficiency. As a result, techniques making use of phosphorescent materials are proposed. Devices that utilizes phosphorescent materials can roughly be divided into two major categories:
(1) Phosphorescent materials are directly used in the light-emitting layer. In this type of display device, light-emitting efficiency (cd/A) will rapidly increase or decrease according to the applied voltage or current. However, the color index may change as luminance increases. Furthermore, most devices using phosphorescent material as the light-emitting layer is hardly able to produce the desired luminance at a low applied voltage;
(2) Phosphorescent material is doped as a guest material inside a host light-emitting material at 1% to 10%. Through the energy transfer of the host material, the guest phosphorescent material is illuminated to produce light. However, the color index may change as the luminance is increased. Ultimately, the degree of increase in luminance and light-emitting efficiency is quite limited.
Accordingly, one object of the present invention is to provide a light-emitting layer and an organic light emitting diode (OLED) device having such a light-emitting layer for increasing the luminance and light-emitting efficiency of the device.
A second object of this invention is to provide a light-emitting layer and an organic light emitting diode (OLED) device having such a light-emitting layer such that color index and light-emitting efficiency can be maintained at a constant level as applied voltage or current is increased. Hence, attenuation of the color index and light-emitting efficiency of the device is minimized.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a luminescence layer. The luminescence layer is an organic material layer comprising hole transporting material and phosphorescent material. The concentration of hole transporting material and phosphorescent material in the luminescence layer is between 40%xcx9c60% by weight. The organic material is either small molecule organic material or polymer organic material such as, for example, an iridium complex compound having an isoquinoline substituted radical. The hole transporting material is a compound having a tribenzoamide structure including, for example, NPB, TPD and TCTA. A hole blocking layer may also be formed over the luminescence layer. The hole blocking layer is fabricated from a material such as BCP, Balq, TAZ or TPBI.
This invention also provides an organic light emitting diode (OLED) device having a substrate, an anode layer, a luminescence layer, a hole blocking layer and a cathode layer. The anode layer is disposed on the substrate and the luminescence layer is disposed on the anode layer. The hole blocking layer is disposed on the luminescence layer and the cathode layer is disposed on over the hole blocking layer. In addition, the luminescence layer is an organic material layer comprising hole transporting material and phosphorescent material. The concentration of hole transporting material and phosphorescent material in the luminescence layer is between 40%xcx9c60% by weight.
In the OLED device of this embodiment, a hole injecting layer and a hole transporting layer may be inserted between the anode layer and the light-emitting layer by selection. The hole injecting layer is positioned between the anode layer and the light-emitting layer while the hole transporting layer is positioned between the hole injecting layer and the light-emitting layer. In addition, an electron injecting layer and an electron transporting layer may be inserted between the hole blocking layer and the cathode layer by selection. The electron injecting layer is positioned between the hole blocking layer and the cathode layer while the electron transporting layer is positioned between the electron injecting layer and the cathode layer.
In the OLED device of this embodiment, the hole injecting layer is fabricated from a material such as CuPc or m-MTDATA. The hole transporting layer is fabricated from a material having a tribenzoamide structure such as NPB, TPD or TCTA. The electron transporting layer is fabricated from a metal complex compound such as AlQ or BeBq2 or a mixture of cyclic compounds including PBD, TAZ or TPBI.
Furthermore, the anode layer on the substrate is a plurality of transparent electrodes each shaped into a longitudinal strip. The anode layer is fabricated using a transparent material such as indiumtin oxide, indiumzinc oxide or aluminumzinc oxide. The cathode layer is a plurality of metallic electrode each shaped into a longitudinal strip. The cathode layer is fabricated using a conductive material such as aluminum, calcium or magnesium-silver alloy. The hole blocking layer is fabricated from a material such as BCP, Balq, TAZ or TPBI.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.